How To Avoid Repair With Keycache?

Question

I have had some experience with optimizing the my.cnf file but my database has around 4 million records (MyISAM). I am trying to restore from a mysqldump but every time I d

Answer 1

"Repair by sorting" uses the filesort routine, which in turn creates several temporary files (usually) in your tmpdir.

If your tmpdir does not have enough space for them, it will revert to "Repair by keycache". This is extremely bad as it's much slower AND creates less optimal indexes.

There are some other conditions but I haven't identified them.

Working out the size of tmpdir you need for filesort() is nontrivial; the format data are stored in the filesort buffer is not the same as MYD files, it typically uses a lot more space.

So if your tmpdir points at a small /tmp (or tmpfs), you might want to change it to a larger /var/tmp - if that exists.